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Reference: A.M. Dart, (1973). A study of the functional relationship between the dorsal column and spinocervical system of the cat. DPhil. University of Oxford.Citable link to this page:

 

A study of the functional relationship between the dorsal column and spinocervical system of the cat

Abstract: ´╗┐Electrophysiological experiments have shown that stimulationof the ipsilateral DLF, caudal to a transection of the dorsalcolumns (at C4), inhibits cells in the dorsal column nuclei.The presence of such inhibition was shown both by focal potential,and single unit, recording. It was found that the amplitude of avolley, conducted down the dorsal columns in response to a shockapplied to the cuneate nucleus and recorded from the killed ends ofdorsal column fibres at the rostral and of a transection of thedorsal columns, was increased by a preceding tetanus applied tothe ipsilateral DLF. This evidence of depolarisation of dorsalcolumn fibre terminals suggests that presynaptic inhibitioncontributes to the inhibition produced by DLF stimulation. Acontribution from postsynaptic inhibitory mechanisms was suggestedby the observation, made on several occasions, that antidromicactivation of a unit from the contralateral mid-brain could beprevented by a preceding shock applied to the ipsilateral DLF.In some oases inhibition of units was produced by squeezing oneor more of the cat's paws; some of these units projected into thecontralateral mid-brain.In addition to an inhibitory action from the ipsilateral DLFon the cells of the dorsal column nuclei, electrophysiologicalexperiments have also demonstrated the presence of an excitatoryaction. The majority of the cells transynaptically activatedstimulation of the DLF were found in the region andminus;3 to +2andnbsp;mm(the obex being aero); however this may have been because themajority of electrode penetrations were also made in this region.Many of the unite so excited were shown to project into thecontralateral mid-brain, thereby demonstrating the existence of agenuine excitatory effect on the dorsal column nuclei. Approximatelyone third of the units excited by stimulation of the DLF were alsoexcited by peripheral mechanical stimulation. In the majority ofcases the effective stimulus was cutaneous stimulation. A numberof units, deep in the cuneate nucleus, ware found to be excitedby noxious mechanical stimulation; no such units wore found inthe gracile nucleus. Only one of those tested was found to projectinto the contralateral mid-brain, suggesting that these units maybe inhibitory interneurones.The excitation and inhibition, produced by stimulation of theipsilateral DLF, were abolished by transection of the DLF. Theywere net affected by transection of the brain stem at a levelimmediately rostral to the dorsal column nuclei. None of the cellstransynaptically activated by stimulation of the DLF were alsoactivated by stimulation of the anterior lobe of the cerebellum;this suggests that dorsal column nuclei cells were not excited bycollaterals of direct spinocerebellar tract fibres.The presence of direct connections between the dorsal columnnuclei and the DLF was demonstrated electrophysiologically by therecording, in the dorsal column nuclei, of short constant latencyresponses with properties indicative of external recordings fromfibres. Whether such fibres were afferent to, or efferent from,the cells of the dorsal column nuclei could not be establishedfrom such recordings. However, evidence for the existence ofboth such categories was found.Some cells in the dorsal column nuclei were antidromicallyactivated by stimulation of the ipsilateral DLF. Some of thesecells were orthodromically activated by afferents coursing in theDLF. The presence of such orthodromic activation of those cellsled to the speculation that the cells with descending projectionsmay synapse, directly or indirectly, with the cells of origin ofthe afferent pathway, and thereby form a feed-back circuit withinthis system.Anatomical experiments have demonstrated the existence ofdirect afferent fibre connections between the DLF and the dorsalcolumn nuclei. Terminal degeneration was found, after lesions ofthe DLF, in the rostral parts of both cuneate and gracile nuclei.The terminal degeneration extended from 1andnbsp;mm caudal to the obex upto the rostral poles of both nuclei. Such anatomical evidence of adirect afferent pathway does not, of course, exclude the presence ofindirect pathways; such pathways, if synapsing before reaching thedorsal column nuclei, would not be demonstrated by anatomical methods.It is not possible, from the results described, to determine whetherthe direct pathway is formed by collaterals from a tract alreadyknown, such as the spinocervical tract, or whether it existsas a separate entity.

Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:This thesis was digitised thanks to the generosity of Dr Leonard Polonsky

Bibliographic Details

Issue Date: 1973Identifiers

Urn: uuid:863d1f5a-0bcd-494c-a2c8-42a7c34d9779

Source identifier: 601870691 Item Description

Type: Thesis;

Language: eng Tiny URL: td:601870691

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Author: A.M. Dart - institutionUniversity of Oxford oxfordCollegeBrasenose College - - - - Bibliographic Details Issue Date: 1973 - Ident

Source: https://ora.ox.ac.uk/objects/uuid:863d1f5a-0bcd-494c-a2c8-42a7c34d9779



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